The pH of FAC in this specification is the value measured according to JIS K-1474, that is the pH value of water measured after adding 2 g of the dry sample (FAC) to 100 ml of pure water followed by mild boiling for 5 minutes and then cooling.
Hitherto, various processes have been proposed for recovering chlorinated hydrocarbon solvents such as tetrachloroethylene, trichloroethane, etc., which are largely used in the steps of dry cleaning, metal cleaning, printing, etc., using granular activated carbon. However, these conventional processes have many faults.
When the aforesaid chlorine-containing solvent is recovered using granular activated carbon, the solvent thus recovered is decomposed due to its easy decomposability. Acids formed by the decomposition of the solvent, and present in the solvent thus recovered, greatly reduce the quality of the recovered solvent. Furthermore, the acids formed by the decomposition of the solvent can cause eroding of the recovery apparatus.
In order to improve such conventional techniques, a process of using fibrous activated carbon as an adsorbent has been proposed.
It is known that fibrous activated carbon shows higher adsorption and desorption rates than conventional granular activated carbon and when using fibrous activated carbon, the decomposition of the recovered solvent is less due to the short desorption time thereof. However, even in the case of using such fibrous activated carbon or FAC, the quality of the recovered product or solvent does not always reach a satisfactory level and the quality deviation of the recovered product depends largely upon the recovery conditions.